The present invention relates to the field of flow control devices and more particularly to a rack and pinion clamping system to regulate flow of fluid or gases in flexible conduits, e.g., medical tubing in extracorporeal dialysis procedures.
Flexible conduits or tubing carrying liquids or gases are used presently in the medical and pharmaceutical industries, as well as in laboratory settings, the chemical industry, the ink and print industries, and for photographic development. These uses are aided by the ability to fixedly open and reliably close the flexible conduit, and in some cases to establish stable partial flow as well.
For instance, many modem medical procedures require the use of flexible tubing to Withdraw fluid from a patient, or to administer fluid to a patient, or to do both. Such procedures include intravenous feeding blood transfusions and blood processing, and both peritoneal dialysis and hemodialysis. Typically, a catheter is temporarily or semi-permanently implanted in the patient, where it is connected in some manner to the appropriate tubing set necessary for the procedure that is to be performed.
In hemodialysis, the patient""s blood is cleansed by drawing it out of the patient though a catheter and passing it through an artificial kidney. Patients in hemodialysis treatment typically require treatment several times a week for several hours each time. In peritoneal dialysis, a peritoneal dialysis solution is infused into the patient""s peritoneal cavity and allowed to reside there for a xe2x80x9cdwell timexe2x80x9d during which blood impurities diffuse through the peritoneal membrane into the dialysis solution. The dialysis solution with the collected impurities is then removed from the peritoneal cavity and discarded.
Many of these procedures require tubing that can be readily opened and closed, either by the medical practitioner or by the patient in the more ambulatory treatment protocols. For example, a peritoneal dialysis patient will often have a semi-permanent implanted catheter in the peritoneal cavity which extends to outside the patient. The exterior end may then be attached to a tubing segment which in turn is usually attached to a connector, perhaps to a bag of fluid for intake, or to a collection device. A reliable system for opening and closing such tubing is essential; a system that also allows for the controlled constriction of the tubing at less-than-fully-open settings would be a bonus.
Pinching and clamping devices are well known, and historically involved a butterfly or alligator clip placed manually along a clampable portion of the tubing or conduit. Rarely was this more than an opened versus closed setting, though certain screw-type clamps were devised to provide adjustable flow and control. These adjustable methods of flow control generally required two hands to apply or adjust, however; most such closure mechanisms are also small and slippery in conditions common in a surgical unit.
An improvement in these devices involved a roller or rolling cam placed in near proximity to the flexible conduit. This was accomplished by pressuring an intermediate constriction device, as in U.S. Pat. No. 4,335,866 (Bujan 1982), or by rolling an externally ribbed wheel or gear in a track, either by direct roller-clamp restriction of the conduit, as in U.S. Pat. No. 3,135,259 (Evans 1964), and U.S. Pat. No. 3,099,429 (Roman 1963), or by rotating a cam that oblated the conduit along its longitudinal line with a V-shaped wedge, as in U.S. Pat. No. 4,911,399 (Green 1990). This latter approach of necessity requires a supporting channel or groove to keep the conduit centered under the impending wedge.
In the operation of existing devices, the user faces a number of problems. Wherever the rolling wheel or clamping means is exposed to facilitate manual control (usually a forward-or-back thumb action along the barrel or case), body fluids or congealing debris can clog the opening, impairing use. Similar material can find its way onto the ribbed wheel, or the operator""s thumb, and cause slippage. When the moveable clamp is other than fixed rigidly in a track over the conduit, lack of traction can keep the clamp from being moved into its fully constricted position. The ability to fix and hold one or more middle positions is difficult, if available at all. Moreover, in some of the existing devices, the conduit must be trapped in a channel to ensure that the rotating clamp can restrict it fully, a channel which often complicates the threading of the conduit through the barrel or body of the flow control device, and adds design expense and detail to the interior of the barrel or case.
The present invention is a flow control device for regulating flow of fluids or gases in flexible conduits, with particular but by no means exclusive application in intravenous delivery systems using flexible tubing, as well as peritoneal dialysis and hemodialysis tubing sets. The flow-control device of the present invention comprises a case or barrel which houses a rack and pinion system which can slidably restrict one or more flexible conduits in the case, from a fully opened to a fully constricted flow. Intermediate restrictive settings may be achieved by a plurality of pre-set engagements comprising a means to xe2x80x9cclick inxe2x80x9d or flexibly and reversibly ratchet along the rack. The case is preferably closed (it could be designed to be waterproof), with manual or machine control of the constrictive settings via a means to slide or rotate the pinion gear assembly, accomplished in one embodiment by an external and ergonomically pleasing slide assembly with ribs or flanges in one embodiment, connecting into the case with an upper rack engaging an adjustable clamping means, preferably a pinion gear assembly comprising rotatable gears, capping the ends of a bisected cylinder shaft.
The present device generally comprises the following: a case or barrel assembly, a rack and pinion assembly interior to the case assembly, and a slidable means that can engage the clamping means of the pinion gear assembly against the flexible conduit. The parts of the invention may all be made by injection molding. The invention may be advantageously pre-assembled, as where the flexible conduit is affixed inside the case to a receiving connector, or threaded by a user through the passage provided in the case. In one embodiment, the case is capped at each end with a port or opening as part of the tubing throughway, said cap preferably comprising a replaceable end piece. In a preferred embodiment, the assembly is sufficiently flexible that it can be snapped together but pried apart by ordinary hand strength.
The case assembly of the invention contains a lower surface for supporting a length of flexible tubing; this surface should be flat or otherwise capable of resisting compression where the pinion gear assembly constricts the conduit. As shown in one embodiment, no guides to seat the conduit are needed along this lower surface so long as the tubing throughway is maintained medially to the teeth of the pinion gear assembly. In a further embodiment, the lower surface has tracks or bilateral gear racks integral to the lower surface; other embodiments may have a single or bilateral rack assembly inserted above the lower surface or otherwise projecting from the side walls.
Whenever by design the clamping face of the pinion gear assembly is unable to achieve a position fully constricting the tubing at some point inside the case, a ramp or other inflexible means may be added along the opposing portion of the lower surface to ensure constriction of the flexible conduit.
The case or barrel is further comprised of opposing side walls extending generally in the vertical plane from and along the longitudinal axis of the lower surface, but possibly cylindrically or irregularly so long as the rack and pinion assembly can readily engage the pinion gear assembly to reliably constrict the conduit therein. Each sidewall may be grooved or shelved or designed to receive the stable placement of either a rack or the axially projecting shafts of the pinion gear assembly, or both. The lower surface may also be used as the lower side of the rack as discussed above, in which case a groove is still provided for the projecting shafts of the pinion gear assembly to facilitate movement of the pinion gear assembly along the racks. The interior of the case should be open enough to allow a portion of flexible tubing to be fixed therein or threaded therethrough. Although the device may be applied at any flexible and clampable portion of the conduit, the embodiment shown in the drawings applies the constricting gear to a point of tubing very near to an end connector. This placement facilitates the clamping constriction, which otherwise may be improved by an opposing ramp opposite the clamping means of the pinion gear assembly to ensure full constriction at one or more points along the lower rack.
The invention further comprises a rack and pinion gear assembly, which when engaged applies an increasingly constrictive clamping means along the longitudinal axis of the lower surface and against the flexible conduit. The clamping means in one preferred embodiment comprises a pinion gear assembly, further comprising a longitudinally bisected cylinder capped at each end with pinion gears. This design facilitates threading of conduit when fully xe2x80x9copenxe2x80x9d while providing for simple open and closed positions and a full and smooth spectrum of intermediate constrictions; an array of other clamping means is known in the art. In this embodiment, the bisected cylinder shaft is integral to and of a smaller radius then the radius of the pinion gears on each end, thus simplifying manufacture of the pinion gear assembly and consuming less space inside the case than the ribbed wheel and projecting cams of the prior art.
In one embodiment, the rack and pinion assembly is designed with an upper and lower rack capturing the pinion gear assembly. As noted, the gear racks may be part of the case, or made part of inserts, or placed along the sidewalls, or optionally with one side wall rack and the other end of the pinion gear assembly shaft free to float forward and back in an open groove on the opposite side wall.
In an embodiment, the lower surface is designed with the gearing tracks of the lower rack on an insertion piece that snaps in just above an outer housing and acts as the lower surface and the lower part of the rack and pinion assembly. This insertion piece can also be designed with ridges or ramps medially bridging the space between the bilateral lower rack tracks to facilitate clamping of the flexible tubing.
One of many valuable improvements of the present invention is found in the upper portion of the rack and pinion assembly. Instead of the open channel design of the traditional rolling wheel and cam, the upper surface of the case in the present invention closes with the side walls. Like the lower rack or tracks, the upper rack can be made integral to the upper surface, or affixed along the upper portion of one or both side walls, or extended inward as part of the slidable assembly, so long as the upper rack slidably engages the pinion gear against the lower rack.
One useful embodiment of the upper surface and upper rack comprises an insertable, slidable assembly wherein the outermost and exposed surface of said assembly has non-skid protrusions or other ergonomically pleasing friction surfaces along its exposed face plate to facilitate thumb or finger control, the innermost surface of said assembly comprises the upper rack engaging the pinion gear assembly, and there is a spacer connecting said outermost surface to said innermost surface; it is this spacer that extends through the slot on top of the case. A well or notch is placed upon the spacer and communicates with one or both side walls and a plurality of opposing nibs thereon to allow for stable xe2x80x9csnapping inxe2x80x9d along the slidable assembly""s continuum from the unconstricted to the fully constricted position. One skilled in the art can readily see that the nibs and notches could be reversed, with the nibs in the slidable assembly space and a plurality of notches along that line in the side wall or walls along the rack. Optionally the plurality of nibs could be placed under the slidable face plate and corresponding notches could be placed along the portion of the outer housing over which the face plate slides. Certain reversible ratchet systems may also be applied.
Another valuable improvement of the present invention involves the stable application of the pinion gear assembly along the upper and lower racks and against the conduit. By moving the slidable assembly linearly, the pinion gear assembly rotates toward and then in contact with the flexible conduit. By proper design, the fully open position is at one end of the rack and pinion assembly, with a means to limit sliding or rotation beyond this point. It is at this extended point that a nib can be placed in the sidewall for contact or xe2x80x9csnap inxe2x80x9d to the notch in the spacer.
By advancing the slidable assembly in the unobstructed direction, engaging the pinion gear assembly, the bisected cylinder of the pinion gear assembly should begin to engage and compress the flexible conduit, in a smooth fashion. Other cylinder shaft designs are known in the art that would apply an irregular radius to achieve the same ends. The nibs and notches of the sidewall and spacer can be designed and marked along this crimping path to provide preset intermediate and stable constriction zones. By continuing to advance the slidable assembly, full constriction of the conduit is achieved, and again a nib and notch can be placed appropriately to mark this far limit of pinion gear assembly rotation, and secure a fixed and xe2x80x9clockedxe2x80x9d position. Properly designed, this sliding mechanism, from open, to partially closed, to fully closed, should be robustly reusable and easily reversible. It is also fully operational by a patient using only one hand. More simply, toggle system or twist knob could be devised to provide the same open/partially constricted/closed sets.
The rack and pinion assembly is designed to be retained within the case. This can be accomplished with capping end pieces, or by affixing or molding the racks into the side walls, the upper and lower surfaces, or along the inserts, with raised barriers and/or ridges at either end of one or both of the racks to limit rotation of the pinion gear assembly, to a designated length of the conduit.
Optionally, the pinion gear assembly could be slided along a series of increasingly high ridges placed upon the lower surface, with the flexible conduit placed along the top of such ridges. Each ridge would constrict the conduit a different set amount, for example, one-fourth, one-half, three-fourths.
Operation of the flow control device, once fully assembled with the flexible conduit in the throughway, is straightforward, presumably using thumb control of the slidable assembly, with only one hand. Machine control could also be applied, perhaps via remote control or timer. Once use of the device is concluded, it can be unhooked and disassembled and cleaned for reuse, or the flexible tubing can be removed and new tubing rethreaded for new use, especially useful where no sterilization is required, such as where non-bodily fluid or reagents are used.